Furnace construction



J.' w. 'rHRocKMoR-roN 2,348,099

FURNAGE CONSTRUCTION Filed sept. 11, 1942 May y2,l 1944.

- INVENTOR. e/o/m g/ or/of? ATTORNEY.

.May 2, 1944- J. w. THRocKMoRToN 2,348,099

j URNAGE CONSTRUCTION 4 Filed sept. 11, 1942 s sheets-sheet 2 IN VEN TOR.

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J. w. THRocKMoR'rN FURNACE CONSTRUCTION Filed Sept. 11, 1942 INVENToR. 77mm? s sheets-Sheet s l 14 TTOPNEY.

Patented May 2, 1944 FUBNACE CONSTRUCTION John W. Throckmorton, Wilton, Conn., assigner to Petro-Chem Process Company Incorporated, a corporation of Delaware Application September 11, 1942, Serial No. 458,049

a claims. (c1. 12e- 276)` My invention relates to new and useful irnprovements in tubular furnace construction.

The invention particularly contemplates vertical tubular furnaces of the type used in the heating of uids both liquids and gases such as the distillation or cracking of hydrocarbons, chemicals, water and like products. Furnaces of this type have a combustion'chamber which encloses a bank or banks of heat exchange tubes. These tubes provide a lcontinuous passage through the combustion chamber for fiuid to be heated. Heating gases are 'supplied to the combustion chamber by a burner or burners ar ranged to distribute the heat uniformly within the furnace. The gases rise vertically, circulating around the tubes and finally exiting via a flue passage opening through the top of the chamber. The fluid usually enters the furnace in a relatively cool condition. As the fluid passes through the heat exchange l'tubes it absorb-s heat from the combustion gases and discharges from the furnace in a relatively heated condition.

I have now developed a construction for a furnace of the above character that is particularly applicable to small furnaces of from 1,000,0005,000,000 B. t. u. capacity.

U-shaped tubes which are interconnected to provide a continuous passage through the furnace for uid to be heated. The tubes straddle the combustion chamber with their legs adjacent opposite walls thereof and with their transverse top portions bridging or spanning the upper end of the chamber.

The bank of heat exchange tubes may be easily i and in the quantity of material used in the fabri cation.

I am aware of prior art constructions wherein heat exchange tubes have been arranged vertically ina combustion chamber with short radius return bend headers at their upper and lower ends.

pressure drop in the fluid travering the heat/exchange unit embodying this invention,.since the U-shape of the tubes provides long radius lbends at the top of the unit. The pressure drop through the long radius bends is much less than In thev combustion chamber I mount a bank of invertedA While the prior art construction4 is generally satisfactory, there is a much lowerv through the conventional short radius return bend headers. l n An important object of my invention is to pro vide in an'upright tubular furnacea? bank of I heat exchange tubes that are uniquely shaped and correlatedto reduce the pressure drop in the uids traversing the bank. f

Another object of my invention is the 'prog vision of an upright tubular furnace thatis susceptible of substantially complete shop lfabrication and assembly, thus eliminating the Aerection costs and considerable weight, as well `as substantially reducing the amount cf'material required in fabrication. i

A further object of my invention i's to'provide a furnace yin which all tubes may be. cleaned from the ground without restorting to any ladders or elevated platforms.

Other objects and advantages 'of my invention' will be apparent during the course of the following description.

In the drawings forming a part of this speci# cation and wherein like numerals are employed to designate like parts throughout the saine,l

Fig. 1 is a front View of a tubular furnace em' bodying -my invention, parts being shown in elevation and parts in Vsection for clearness of illustration,

Fig. 2 is a transverse sectional view, vtaken'on the line 2-2 of Fig. 1,

Fig. 3 is a transverse sectional view,` taken on the liner 3;-3 of Fig. 1,

'Y Fig. 4 is'a'front view'of a modified form of the furnace,'parts being shown in section V,for clearness of illustration, Fig. 5 is a vertical sectional view of the bank:

of heat exchange tubes shown in'Fig. 4,

Fig. 6 is a transverse sectional view, taken on` the line 6 6 of Fig. 5,

Fig. 7 is a fragmentary transverse sectional view taken on the line 1-1 of Fig. 5, y Fig. 8 is a fragmentary, vertical sectional view taken on the line 8-8 of Fig. 7, Fig. 9 is a fragmentary vertical sectional view i taken on the line 9 9 `of Fig. 6, and

Fig. 10 is a fragmentary vertical sectional view of still another modification of the furnace.

In the accompanying drawingswherein for the purpose cf illustration is shown a preferred embodiment of my invention, the numeral I51 designates a cylindrical metallic casing linedl with a refractory Ymaterial I6. Thev casing'has a bottom I5a and the bottom is` also lined with H refractory material 16a. The top of the casing is closed by the iiared lower end 11a of a stack or flue passagel'l. The space enclosed within the casing comprises a combustion chamber. Combustion gases are supplied to the chamber by a burner I8 extending through the bottom of the furnace. The entire structure rests upon a suitable supporting frame I9.

Within the combustion chamber is a bank of inverted U-shaped heat exchange tubes 2D. As shown in Fig. 2, the widths of the U-bends Ell progressively decrease toward the ends of the bank so that the bank is essentially circular in transverse section. The lower ends of the tubes are arranged in a circle adjacent the wall of the combustion chamber and the tubes are interconnected by return bends 2l or any suitable design for continuous flow of fluid through the bank. I prefer that the lower ends of the tubes extend through the bottom of the furnace soi that the headers 2| are readily accessible. Suitable covers 22 having'hinged bottoms 22a. en-

close the headers. VEach of the headers'has aV clean-out port normally closed by a removable plug. Solids in theV uid deposit on the walls of the tubes and .these solids must be removed periodically. The` construction here illustrated provides for easy cleaning of the tubes since it is necessary only to open the hinged bottoms 22a, remove the clean-out plugs and insert the cleaning element. The cleaner `will pass through the upper bent tube section, since it has an essentially long radius. Y Y

Fluid to be heated enters the furnace through an inlet pipe 23 which connects with the bank of heat exchange tubes anddischarges from the furnaces through a delivery -pipe '2li connected at the opposite end of the bank of tubes. The fiuid usually enters thefurnace in a relatively cool condition and discharges therefrom vin a relatively heated condition. As vthe fluid traverses the bank of heat exchange ltubes it absorbs heat from the combustion gases. By plac-v ingthe top bends of the tubes transversely across the combustion chamberand'directly in the path of the flue gas, the operation vof the furnace to absorb heat from the'combustion gases is particularly eicient. vision of long radius 'bends at the top of the heat exchange bank greatly reduces the pressure drop in the fluid. Y

Fig. 4 shows a construction-wherein the lower ends 0f the tubes 2! connect with an annular tubular manifold 25 supported by the bottom 15a of the` furnace. Vertical partitions 26 at opposite sides of the manifold separate-the same into chambers or compartments 25a and 25h..

One leg of each heat exchangetube communicates with chamber 25a and the other leg thereof communicates with chamber 25h. Pipe 23` is connected to the header 21 which forms an cutlet from chamber 25a and pipe 24 is connected to the header 28 forming an outlet from chamber 25h. As the fluid enters chamber 25a'throug`h pipe 23 it strikes a horizontal baffle kplate 29 which spreads it evenly through the chamber and causes a substantially even distribution of the fluid in each of the heat exchange tubes. Manifestly all of the tubes will be in parallel and the fluid in chamber 25a will be transmitted to section 25h; simultaneously through each of the tubes This Vunique arrangement provides a large number of tubes to be placed in parallel ow and provides excellent distribution of the fluid.

Furthermore, there is a much lower'pressure drop in the fluid traversing the heat exchange In addition, ithe pro' as a unit for cleaning or repair.

In Fig. 10 I show a construction wherein an economizer is provided in a stack I1 so that low flue gas temperature and high eiciency are obtained. The economizer, which may be associated with either the furnace shown in Fig. l or the furnace shown in Fig. 4, comprises inverted U-shaped tubular members 30 having outwardly bent end portions 30a and 30o which extend exteriorly of the stack. Inlet pipe 23 is connected to the end portion 30a and the end portion 3619 is connected to an upward extension 26a, of the heat exchange tubes by a connection 3l.' Economizer 30 and stack Il are preferably made as a unit, and connection 3l and inlet pipe 23 are detachably connected to the end portions 3a. and 30h so that the stack and economizer may be applied to or removed from the furnace as a unit. When the stack and economizer have been removed, easyV access may be had to the bank of heat exchange tubes 2i). The economizer may bean air heater for preheating the air to the burner instead of a preheater for the fluid charge to the furnace.

The bank of heat exchange tubes 2i] and particularly the lower portions thereof will be subjected chiefly to radiant heat. Heat will be transferred from the gases to the fluid inthe heat exchange tubes 20. Obviously then the gases will become cooler as they rise in the combustion chamber. However, considerable heat will be carried by the gases into the convection section or stack Il. By mounting the economizer Si! in the stack a substantial portion of this heat will be absorbed by the fluid traversing the economizer. At least a portion of the ec'onomizer tubes have radial ns 3Go which provide extended surfaces for increasing heat absorption. Since the fluid flowing through the economizer will be relatively cool, it will be particularly efcient in absorbing heat from the exhaust ccmbustion gases and will thereby enter the comey bustion chamber in a preheated condition, thus' increasing the efficiency of the furnace.

It will thus be seen that I have'achieved the' `the heat exchange units are uniquely constructed so that there is very little pressure drop in the fluid as it iiows through the furnace.

t will be understood that certain features andsubcombinations are of utility and may be em-v ployed without reference to other features and sub-combinations. This is contemplated byand is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details vshown and described.

Having thus described my invention, I claim:

1. A furnace construction comprising a cylindrical reinforced wall of refractory material providing a combustion chamber, a source of heat Within the chamber, a bank of inverted U-shaped heat exchange tubes of varying radii Vbridging the top of the combustion chamber and serially interconnected to provide a continuous fluid passage through the chamber, the straight portions of said U-shaped tubes arranged adjacent the Wall of said chamber, and inlet and outlet pipes communicating with the U tubes having the smallest radii.

2. A furnace construction comprising a reinforced cylindrical wall of refractory material providing a combustion chamber, a source of heat Within said chamber, a bank of inverted U- shaped tubes of varying radii, the straight portions of the tubes adjacent the wall of the chamber and the curved portion bridging the chamber, said U-shaped tubes serially connected to provide a continuous passage through the chamber, inlet and outlet pipes connected to the tube bank, and spacing members bridging thetubes diametrically across the chamber to hold the tubes in xed relationship with respect to each other.

3. A furnace construction comprising a reinforced cylindrical wall of refractory material providing a combustion chamber, a source of heat within the chamber, a removable nue section enclosing the top of a combustion chamber, a unitary prefabricated bank of inverted U- shaped heat exchange tubes including inlet and outlet connections said bank removably mounted into the combustion chamber from above, the straight portions of the U-shaped tubes adjacent the combustion chamber Wall and the curved portions bridging the combustion chamber when installed.

JOHN W. THROCKMORTON. 

